Charge-transporting thin-films are used in organic electroluminescence (organic EL) devices.
Processes for forming such charge-transporting thin-films are broadly divided into dry processes such as vapor deposition and wet processes such as spin coating. These processes can be selectively used as appropriate according to the surface area of the thin-film to be formed and the solubility in organic solvents of the material to be rendered into a thin-film.
Generally, between the positive electrode and the emissive layer of an organic EL device, two layers—a layer called the hole injection layer and a layer called the hole transport layer—are arranged in this order from the positive electrode side. Providing two such layers makes efficient charge transport possible, enabling an organic EL device having high brightness characteristics to be obtained (see, for example, Non-Patent Document 1).
Yet, on the other hand, organic EL device production processes also have the drawback that independent steps are normally required to form these layers.
Lately in the field of electronic devices, there exists a desire, in order to efficiently manufacture devices at a high yield, for process simplification and greater simplicity in the device structure.
In particular, by replacing a functional multilayer film obtained by stacking a plurality of films in the device with a single film, not only can the manufacturing process be simplified, it is also possible to directly simplify the device structure. Hence, in connection with various electronic devices, there exists a desire for materials capable of producing functional single films that can be substituted for existing functional multilayer films.
In the field of organic EL devices as well, there is an increasing desire for materials that can replace a functional multilayer film typically composed of a hole injection layer and a hole transport layer with a single film.